It is well known that ammonium thiosulfate is acutely hygroscopic and unstable, and as a result, tends to agglomerate and cake, a phenomenon which is also known for other ammonium salts such as, for example, ammonium sulfite. This tendency to clump or cake represents a serious disadvantage since the caked salt must be mechanically crushed to enable measurement and dosage thereof.
However, a free flowing stable ammonium thiosulfate has been highly desired for the production of stable so-called "rapid-fix" salt mixtures, particularly in the photographic processing field, which are portable, easily measurable and readily soluble in water.
Towards this end, prior attempts to alleviate the ammonium thiosulfate caking problem have encompassed both physical treatments of the ammonium thiosulfate as well as blending of additives thereto. For instance, U.S. Pat. No. 5,055,384 describes blending ammonium thiosulfate with an alkali disulfate and thereafter milling the blend to within a average particle diameter of from 150 to 300 .mu.m in order to improve the flowing properties of the ammonium thiosulfate. On the other hand, U.S. Pat. No. 3,512,929 discloses blending dry crystalline ammonium thiosulfate with small amounts of sodium thiosulfate in order to discourage the clumping behavior of the ammonium thiosulfate.
On the other hand, alkyl aryl sulfonate compounds are widely-known as a detergent agent, e.g., as seen in U.S. Pat. Nos. 2,515,577 and 2,579,380. Also, sodium salts of formaldehyde condensation products of betanaphthalene sulphonic acid have also been proposed for use as a dispersing agent for chlorinated lime powder as described in U.S. Pat. No. 2,589,108. Additionally, use of alkyl naphthalene sulfonates as a wetting agent for mixtures of alkali oxalate and anhydrous alkali thiosulfate is also suggested in U.S. Pat. No. 2,578,075.
In addition to the caking problem another problem heretofore associated with alkali thiosulfate was that the material was not readily soluble or dissolved and formed a turbid solution due to inadvertent liberation of decomposition products, such as sulfur particulates. In this regard, U.S. Pat. No. 3,350,168 describes blending ammonium salts of weak acids with the ammonium thiosulfate in an effort to prevent liberation of such decomposition products. As another approach, U.S. Pat. No. 2,203,903 describes combining alkali thiosulfate with sodium sulfite, sodium acetate, citric acid and alum to inhibit formation of sulfur in the fixing bath from the decomposition of the thiosulfate.